1. Field of the Invention
The present invention relates to a method of fabricating a liquid crystal display device, and more particularly, to a manufacturing line of a liquid crystal display device using a drop-filling and fabricating method thereof, by which liquid crystal alignment failure can be repaired.
2. Discussion of the Related Art
As information society rapidly develops, the demand for a display technology is increasing in various ways. A variety of flat display devices are designed to meet such a demand and many efforts are made to develop such a flat display device as LCD (liquid crystal display device), PDP (plasma display panel), ELD (electroluminescent display), VFD (vacuum fluorescent display), and the like. Some of the flat display devices are already applicable to various equipments.
By replacing CRT (cathode ray tube), which cannot be used as mobile image display devices, LCDs provide excellent features including excellent image quality, lightweight, compact size, and low power consumption, thereby becoming the most popular device of the various flat display devices. Moreover, LCDs are also applicable as a TV set to receive and display broadcast signals, a computer monitor, and the like, as well as a portable notebook computer monitor.
A liquid crystal display device mainly consists of a liquid crystal display panel and a drive unit applying a drive signal to the liquid crystal display panel. The liquid crystal display panel consists of first and second glass substrates assembled to each other to leave a predetermined distance from each other, and a liquid crystal layer injected between the first and second glass substrates.
A plurality of gate lines arranged in one direction with a predetermined distance therebetween, a plurality of data lines arranged with a predetermined interval therebetween in a direction perpendicular to the respective gate lines, a plurality of pixel electrodes formed in pixel areas provided by the crossing of the gate and data lines, respectively, and a plurality of thin film transistors for transferring signals of the data lines to the corresponding pixel electrodes by being switched by signals of the gate lines, respectively are formed on the first glass substrate (TFT array substrate).
A black matrix layer enabling light to be transmitted to the pixel areas only, an R/G/B color filter layer, and a common electrode for implementing an image are formed on the second glass substrate (color filter substrate).
The first and second glass substrates, between which a predetermined space is provided by spacers, are assembled to each other by a sealant having a liquid crystal inlet. Liquid crystals are then injected in the predetermined space via the liquid crystal injection inlet.
In doing so, when the liquid crystal inlet is dipped in liquid crystals while a vacuum state of the predetermined space is maintained, liquid crystals are injected between the two substrates by an osmotic action. After completion of the liquid crystal injection, the liquid crystal inlet is sealed with a sealant.
However, the related art fabricating method of an injection type liquid crystal display device has the following disadvantages or problems.
First, after completion of cutting into unit panels, the vacuum state of the gap between the two substrates needs to be maintained to inject liquid crystals therein by dipping the liquid crystal inlet in the liquid crystals. Hence, the liquid crystal injection takes a considerably long time to reduce productivity.
Secondly, in case of fabricating a wide liquid crystal display device, the liquid crystal injection method may not completely fill the liquid crystal panel with liquid crystals which causes failure of the device.
Thirdly, the corresponding process is complicated and requires quite a long processing time. The corresponding process requires various liquid crystal injection equipment, which occupies an excessive installation space.
Hence, much research and development has been directed to a method of fabricating a liquid crystal display device using drop-filling.
A method of fabricating a liquid crystal display device using drop-filling according to a related art is explained as follows.
FIG. 1 is a block diagram of a process line using liquid crystal drop-filling according to a related art, and FIGS. 2A to 2E are cross-sectional diagrams of a method of fabricating a liquid crystal display device using drop-filling according to a related art.
First, in a method of fabricating a liquid crystal display device using drop-filling, instead of forming one liquid crystal display panel on one glass substrate, a plurality of liquid crystal display panels are preferably designed on a mother substrate greater than one unit liquid crystal display panel. A thin film transistor array is formed on each liquid crystal display panel area on a first mother substrate, and a color filter array is formed on each liquid crystal display panel area on a second mother substrate.
An alignment layer for liquid crystal alignment is formed on each of the first and second mother substrates. Rubbing is then performed on the alignment layer. Liquid crystals are dropped on the corresponding liquid crystal display panel areas of the first or second mother substrate. A sealant and Ag dots are dispensed on a periphery of the liquid crystal display panel area. The first and second mother substrates are then assembled to each other. The assembled substrates are cut into unit liquid crystal display panels to be processed.
Namely, a manufacturing line for drop-filling according to a related art, as illustrated in FIG. 1, includes vacuum alignment equipment 10 for assembling a first mother substrate having thin film transistor arrays and a second mother substrate having color filter arrays in a vacuum state after completion of liquid crystal dropping and sealant coating thereon, a UV sealant hardener 20 for hardening the sealant between the assembled substrates by UV-hardening, thermosetting equipment 30 for thermosetting the UV hardened substrates, and a cutter 40 for cutting the thermoset substrates into unit liquid crystal display panels.
A process carried out in the vacuum alignment equipment 10 is explained in detail by referring to FIGS. 2A to 2E as follows.
In FIG. 2A, a UV-hardening sealant 1 is coated about 30 μm thick on a portion of a first glass substrate 3 having thin film transistor arrays formed thereon. Liquid crystals 2 are dropped on the first glass substrate 3 inside a border formed by the sealant 1 (over the thin film transistor arrays). In coating the sealant 1, no liquid crystal inlet is provided to the sealant 1.
The first glass substrate 3 is loaded on a horizontally movable table 4 within a vacuum chamber ‘C’. A lower surface of the first glass substrate 3 is held by a first vacuum holder 5 using vacuum suction to be fixed thereto.
Referring to FIG. 2B, a lower surface of a second glass substrate 6 having color filter arrays formed thereon is held by a second vacuum holder 7 using vacuum suction to be fixed thereto. The vacuum chamber ‘C’ is then closed to provide a vacuum state therein. The second vacuum holder 7 is vertically lowered to leave a distance of 1 mm from the first glass substrate 3. The table 4 having the first glass substrate 3 loaded thereon is horizontally moved to preliminarily align the first and second glass substrates 3 and 6.
Referring to FIG. 2C, the second vacuum holder 7 is vertically lowered to contact the second glass substrate 6 with the liquid crystals 2 or sealant 1.
Referring to FIG. 2D, the second vacuum holder 7 is vertically lowered so that the second glass substrate 6 is attached to the first glass substrate 3 via the sealant 1. A illustrated in FIG. 2E, the second glass substrate 6 is pressurized to leave a distance of 5 μm from the first glass substrate 3.
The assembled substrates are taken out of the vacuum alignment equipment 10 and are then transferred to the UV-sealant hardener 20. A masking is formed on the assembled substrates to expose the sealant 1 only. UV light is applied to the sealant 1 only to perform a first hardening on the sealant 1.
The assembled substrates are moved to the thermosetting equipment 30 from the UV-sealant hardener 20. The sealant 1 is then thermoset for about 60 minutes at 120° C. in the thermosetting equipment 30.
The assembled substrates are then transferred to the cutter 40 to be cut into a plurality of unit liquid crystal display panels. Although not shown in the drawings, the unit liquid crystal display panels are then further processed by other processing equipment. A test process is also performed on the processed panels by test equipment.
By the test process, various characteristics of the liquid crystal display panel are checked. In doing so, a domain failure (alignment failure) is checked. Namely, in the rubbing process, a surface of the alignment layer formed on the substrate is rubbed by a rubbing cloth that rotates at a uniform pressure and speed so that polymer chains on the surface of the alignment layer can be aligned in one direction to determine an alignment direction of liquid crystal molecules. In doing so, the alignment direction of one portion having a weak alignment force deviates at a different angle from that of the other portion, whereby the domain failure takes place.
Hence, a worker manually sorts the liquid crystal display panel. After aging has been performed on the sorted panel, the aged panel is put on an iron plate to be rapidly cooled. And, the domain failure is checked again.
However, the related art method of fabricating the liquid crystal display device using drop-filling has the following problem or disadvantage.
First of all, after the assembled substrate have been cut into the unit liquid crystal display panels, each of the unit liquid crystal display panels is tested by a worker. If the domain failure is found, the worker manually sorts the domain-failing liquid crystal display panel. After aging has been performed on the sorted panel, the aged panel is put on an iron plate to be rapidly cooled. And, the domain failure is checked again. Such a process is repeated until the domain failure is overcome.
Hence, the domain failure test is performed on each liquid crystal display panel, thereby needing a long test time and more manpower.